Machines utilizing impact as a means for effecting a working operation applying a large amount of substantially instantaneous (high energy rate) energy comprise a striking mass constituted usually by a double-acting piston capable of movement in either direction and the tool which transmits the kinetic energy of the striking mass at the moment of impact to the point where this energy is utilized by conversion to a shock wave.
In normal use the extremity of the tool, which is located outside the machine, is maintained in contact with the material to which the impact is delivered in such manner that the drills of energy is accomplished under the best working conditions. Such impact machines include fluidpowered breakers, crills, chisels, hammers, and like percussion devices which may be hand-held or support or vehicle mounted.
In carrying out impact work it has been found that the return movement of the tool presents certain difficulties. This is particularly so in the drilling of a bore of a considerable depth or in the use of a demolition tool in material of high impact strength. It is then advantageous to be able to employ the trains of shock waves previously used to break the material to subject the tool to an extracting force which facilitates the withdrawal of the tool.
Unfortunately, in conventional machines, the first component affected by the passage of the shock wave is the part of the machine effecting the return of the tool and if particular precautions are not taken this machine part is destroyed and often with it other parts of the machine. Thus in conventional machines a clearance is provided to separate the tool sufficiently from the striking mass when the latter effects a return movement. During the supplementary stroke of the striking piston, an absorption device or so called dash pot which absorbs the kinetic energy of the piston, comes into play.